The invention relates to novel catalyst systems that may be used in a process for the preparation of copolymers of carbon monoxide and one or more ethylenically unsaturated compounds.
Copolymers of carbon monoxide and one or more ethylenically unsaturated compounds are known. Typically they have a high molecular weight and a linear structure. In the copolymer molecules the units originating from carbon monoxide substantially alternate with the units originating from the ethylenically unsaturated compound(s). If the copolymer molecules comprise units derived from different ethylenically unsaturated compounds (A,B . . . etc.), these units which alternate with the units derived from carbon monoxide, are also usually randomly distributed over the copolymer molecule.
Various methods for preparing the said copolymers have been described in the art. These methods generally involve reacting the monomers, i.e. carbon monoxide and the ethylenically unsaturated compound(s) under polymerization conditions in the presence of a suitable catalyst system.
Much effort has been put into the development of active catalyst systems in order to ensure that the copolymers are formed at a high polymerization rate. Furthermore, it is considered desirable to produce copolymers with a high molecular weight, in view of the envisaged uses for the copolymers. Therefore it was investigated which reaction conditions would be advantageous in these respects and which other factors could influence the polymerization rate and/or the molecular weight of the copolymers produced. One of the reaction variables considered likely to be of significance is the reaction temperature. It has been observed that the temperature at which the polymerization is carried out, affects the activity of the catalyst system, as well as the molecular weight of the copolymers obtained. Unfortunately, the effect a certain change in reaction temperature has on the activity of the catalyst system is opposite to the effect this change has on the molecular weight of the copolymers produced. Thus, an increase in reaction temperature under otherwise similar reaction conditions, results in an increase in polymerization rate, but in a decrease in the molecular weight of the copolymer obtained.
Another factor of relevance for obtaining high polymerization rates is the structure of the components on which the catalyst system is based. It has been established that active catalyst systems usually are based on compounds of metals of Group VIII of the Periodic Table, on a source of anions and on bidentate ligands.
In this connection many bidentate ligands were investigated, whereby favorable results were obtained with ligands which can be defined by the formula R.sup.1 R.sup.2 M.sup.1 --R--M.sup.2 R.sup.3 R.sup.4 wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 represent optionally substituted hydrocarbyl groups, M.sup.1 and M.sup.2 represent atoms of elements of Group VA of the Periodic Table and R is a bivalent bridging group.
In EP-A-222454 it is disclosed that the performance of catalysts comprising a bidentate ligand of this category, is enhanced if at least one of the groups R.sup.1, R.sup.2, R.sup.3 and R.sup.4 represents an aryl group containing a polar substituent at the position, para to M.sup.1 or M.sup.2. Further research has shown that the performance of the catalyst can be further enhanced by incorporating a bidentate ligand wherein at least one of the R.sup.1 to R.sup.4 groups represents an aryl group containing a polar substituent in a position ortho to a phosphorus atom which is represented by M.sup.1 and M.sup.2. The improved catalytic performance can be experimentally demonstrated by comparing the results obtained with 2-methoxy and 2,4-dimethoxyphenyl groups in the bidentate ligands with the results obtained with 4-methoxyphenyl and non-substituted phenyl groups in the bidentate ligand.
Surprisingly it has now been found that the performance of the catalyst can be further improved by using a catalyst system based on bidentate ligands of the aforesaid category, which contain one or more aryl groups, i.e. R.sup.1 . . . R.sup.4, carrying specific substituents at one or both ortho positions and also at a meta or para position, with respect to M.sup.1 or M.sup.2.